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Autosomal Recessive Transmission of a Rare KRT74 Variant Causes Hair and Nail Ectodermal Dysplasia: Allelism with Dominant Woolly Hair/Hypotrichosis
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Immunology, Genetics and Pathology, Medical Genetics. Uppsala University, Science for Life Laboratory, SciLifeLab.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Immunology, Genetics and Pathology, Medical Genetics. Uppsala University, Science for Life Laboratory, SciLifeLab.ORCID iD: 0000-0003-4185-7409
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2014 (English)In: PLoS ONE, ISSN 1932-6203, Vol. 9, no 4, e93607- p.Article in journal (Refereed) Published
Abstract [en]

Pure hair and nail ectodermal dysplasia (PHNED) comprises a heterogeneous group of rare heritable disorders characterized by brittle hair, hypotrichosis, onychodystrophy and micronychia. Autosomal recessive (AR) PHNED has previously been associated with mutations in either KRT85 or HOXC13 on chromosome 12p11.1-q14.3. We investigated a consanguineous Pakistani family with AR PHNED linked to the keratin gene cluster on 12p11.1 but without detectable mutations in KRT85 and HOXC13. Whole exome sequencing of affected individuals revealed homozygosity for a rare c.821T> C variant (p.Phe274Ser) in the KRT74 gene that segregates AR PHNED in the family. The transition alters the highly conserved Phe274 residue in the coil 1B domain required for long-range dimerization of keratins, suggesting that the mutation compromises the stability of intermediate filaments. Immunohistochemical (IHC) analyses confirmed a strong keratin-74 expression in the nail matrix, the nail bed and the hyponychium of mouse distal digits, as well as in normal human hair follicles. Furthermore, hair follicles and epidermis of an affected family member stained negative for Keratin-74 suggesting a loss of function mechanism mediated by the Phe274Ser substitution. Our observations show for the first time that homozygosity for a KRT74 missense variant may be associated with AR PHNED. Heterozygous KRT74 mutations have previously been associated with autosomal dominant woolly hair/ hypotrichosis simplex (ADWH). Thus, our findings expand the phenotypic spectrum associated with KRT74 mutations and imply that a subtype of AR PHNED is allelic with ADWH.

Place, publisher, year, edition, pages
2014. Vol. 9, no 4, e93607- p.
National Category
Medical Genetics
URN: urn:nbn:se:uu:diva-225058DOI: 10.1371/journal.pone.0093607ISI: 000334160900039OAI: diva2:728633
Available from: 2014-06-24 Created: 2014-05-27 Last updated: 2016-02-29Bibliographically approved
In thesis
1. Genetics of Two Mendelian Traits and Validation of Induced Pluripotent Stem Cell (iPSC) Technology for Disease Modeling
Open this publication in new window or tab >>Genetics of Two Mendelian Traits and Validation of Induced Pluripotent Stem Cell (iPSC) Technology for Disease Modeling
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Novel technologies for genome analysis have provided almost unlimited opportunities to uncover structural gene variants behind human disorders. Whole exome sequencing (WES) is especially useful for understanding rare Mendelian conditions, because it reduces the requirements for a priori clinical data, and can be applied on a small number of patients. However, supporting functional data on the effect of specific gene variants are often required to power these findings. A variety of methods and biological model systems exists for this purpose. Among those, induced pluripotent stem cells (iPSCs), which are capable of self-renewal and differentiation, stand out as an alternative to animal models.

In papers I and II we took advantage of WES to identify gene variants underlying autosomal recessive pure hair and nail ectodermal dysplasia (AR PHNED) as well as autosomal dominant familial visceral myopathy (FVM). We identified a homozygous variant c.821T>C (p.Phe274Ser) in the KRT74 gene as the causative mutation in AR PHNED, supported by the fact that Keratin-74 was undetectable in hair follicles of an affected family member. In a family segregating FVM we found a heterozygous tandem base substitution c.806_807delinsAA (p.(Gly269Glu)) in the ACTG2 gene in the affected members. This novel variant is associated with a broad range of visceral symptoms and a variable age of onset.

In Paper III we explored the similarity between clonally derived iPSC lines originating from a single parental fibroblast line and we highlighted the necessity to use lines originating from various donors in disease modeling because of biological variation. Paper IV focused on how the genomic integrity of iPSCs is affected by the choice of reprogramming methods. We described several novel cytogenetic rearrangements in iPSCs and we identified a chromosome 5q duplication as a candidate aberration for growth advantage.

In summary, this doctoral thesis brings novel findings on unreported disease-causing variants, as supported by extensive genetic analysis and functional data. A novel molecular mechanism behind AR PHNED is presented and the phenotypic spectrum associated with FVM is expanded. In addition, the thesis brings novel understanding of benefits and limitations of the iPSC technology to be considered for disease modeling.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 54 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1078
Disease modeling, Mendelian disorders, iPSC, Whole exome sequencing, Transcriptome sequencing
National Category
Genetics Cell Biology Medical Genetics
Research subject
Medical Science
urn:nbn:se:uu:diva-246228 (URN)978-91-554-9184-0 (ISBN)
Public defence
2015-04-24, Fåhraeussalen, Rudbeck Laboratoriet, Dag Hammarsjöldsväg 20, Uppsala, 09:15 (English)
Available from: 2015-04-01 Created: 2015-03-03 Last updated: 2015-09-24

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